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Research Papers

Full Parametric Characterization of LSM/LSM-YSZ Cathodes by Electrochemical Impedance Spectroscopy

[+] Author and Article Information
Rui Antunes

Instituto Politécnico de Setúbal,
Escola Superior de Tecnologia do Barreiro,
Rua Américo Silva Marinho,
Lavradio 2839-001, Portugal
e-mail: ruimma@gmail.com

Janusz Jewulski

Institute of Power Engineering,
Fuel Cells Department,
36 Augustówka Str.
Warszawa 02-981, Poland
e-mail: janusz.jewulski@ien.pl

Tomasz Golec

Institute of Power Engineering,
Thermal Processes Department,
36 Augustówka Str.,
Warszawa 02-981, Poland
e-mail: tomasz.golec@ien.pl

Contributed by the Advanced Energy Systems Division of ASME for publication in the JOURNAL OF FUEL CELL SCIENCE AND TECHNOLOGY. Manuscript received May 13, 2013; final manuscript received August 4, 2013; published online November 5, 2013. Editor: Nigel M. Sammes.

J. Fuel Cell Sci. Technol 11(1), 011007 (Nov 05, 2013) (7 pages) Paper No: FC-13-1048; doi: 10.1115/1.4025533 History: Received May 13, 2013; Revised August 04, 2013

The contributions of the individual process steps of the cathode resistance were determined experimentally, directly from impedance spectra obtained from symmetrical cells. The symmetrical cells have architecture/structure consisting of YSZ electrolyte and a double layer cathode LSM-LSM/YSZ. The investigations were carried out in the temperature interval from 650 to 900 °C. The cathode processes steps activation energies obtained were 1.16 eV, 1.1 eV, and 0.09 eV (diffusion), respectively, which is in relatively good agreement with literature values. To understand the role of layer cathode thickness on electrochemical performance, electrical impedance spectra from symmetric LSM/YSZ/LSM cells were deconvoluted to obtain the key electrochemical components of electrode performance, namely ohmic resistance (RΩ), two low frequency processes related with chemical adsorption and dissociative reaction of O2 (Rp1 and Rp2), and bulk gas diffusion (W, finite warburg) through the electrode pores. The model used has Voight structure with three times constant. These parameters were then related to features, such as contact layer thickness, function layer thickness, and temperature. It was found that polarization resistance is highly dependent on the thickness of the contact layer (Rp1 and Rp2). All deconvoluted parameters are validated by using the appropriate physicochemical model.

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References

Figures

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Fig. 1

Double-layer cathode (cross section): CL—contact layer (La0,8Sr0,2MnO3); FL—functional layer (LSM + TZ3Y); E—electrolyte (TZ3Y)

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Fig. 2

Experimental setup for EIS

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Fig. 3

Scanning electron micrographs of interfaces of symmetrical cell: (a) cross section of the interface LSM/LSM-TZ3Y/TZeY; (b) cross section of the interface LSM/LSM-TZ3Y

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Fig. 4

(a) Symmetrical cell LSM-LSM/YSZ at 650 °C. Cell configuration: FL—8 μm; CL—14 μm. Equivalent circuit model fitted: L-RΩ-(R1Q1)-(R2Q2). Mean fitting error less than 0.5% and maximum local fitting error less than 3%. (b) Symmetrical cell LSM-LSM/YSZ at 750 °C. Cell configuration: FL—8 μm; CL—14 μm. Equivalent circuit model fitted: L-RΩ-(R1Q1)-(R2Q2)-W. Mean fitting error less than 0.5% and maximum local fitting error less than 3%.

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Fig. 5

Symmetrical cell LSM-LSM/YSZ at 300 °C. High-frequency spectrum: 3 MHz to 150 Hz. Cell configuration: FL—8 μm; CL—58 μm. Equivalent circuit model fitted: L-RΩ-(R1Q1)(R2Q2). Mean fitting error less than 1% and maximum local fitting error less than 5%.

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Fig. 6

Three times constant Voigt model. RΩ—ohmic resistance; L—inductance element; Rp—polarization resistance; CPE—constant phase element; W—finite diffusion element.

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Fig. 7

Capacitance associate to process 1 versus contact layer thickness. Set of cells with function layer thickness around 8 μm.

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Fig. 8

Polarization resistance associate to process 1 (Rp1) versus contact layer thickness. Set of cells with function layer thickness around 8 μm.

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Fig. 9

Polarization resistance associate to process 2 (Rp2) versus contact layer thickness. Set of cells with function layer thickness around 8 μm.

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Fig. 10

Capacitance associate to process 2 versus contact layer thickness. Set of cells with function layer thickness around 8 μm.

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Fig. 11

Effective binary diffusion DO2-N2eff as function of temperature T1.5 for cells 1FL2CL (8 μm:18 μm) and 1FL4CL (8 μm:59 μm)

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Fig. 12

Nernst layer thickness dN as function of contact layer thickness, thickness CL, for cells 1FL2CL (8 μm:18 μm) and 1FL4CL(8 μm:59 μm)

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Fig. 13

Polarization resistance associate to process 1 versus 1/T (Arrhenius plot). Symmetrical cells 1FL +2CL (8 μm:18 μm) and 1FL +4CL (8 μm:59 μm).

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Fig. 14

Polarization resistance associate to process 2 versus 1/T (Arrhenius plot). Symmetrical cells 1FL +2CL (8 μm:18 μm) and 1FL +4CL (8 μm:59 μm).

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